After another call with PayPal, I got a tech that had been there long enough to know the evolution of their products. I was told that I am using Payments PayFlow Pro... and they are now referring to it as "Payments Pro" and and phasing out the old Payments Pro that used the API's. I even have a welcome letter from a few months ago where PayPal welcomed my client to "PayPal Payments Pro" even though we were using "PayPal PayFlow Pro." Changing the webassist settings to PayPal PayFlow Pro in webassist and using the merchant login information did the trick. Maybe I should have known this...but I can't imagine why. Anyway, I hope this helps someone else out.
FYI - Another clue was in PayPal where you create your API credentials. It used to say something about creating credentials for shopping carts and third party solutions. It now says, "Manage API credentials to integrate PayPal Express Checkout." No mention of Payments Pro or other PayPal products.